Yeast RNA-Protein Interactions Generate Beer Haze

Beer haze is a main visual attribute for beer styles such as wheat beers (e.g., Belgian Wit, German Weizen) and New England IPA. RNA-rich extracts from brewer yeast cells can generate turbidity in beer. The addition of yeast-derived extract or pure yeast RNA to beer generates a haze consisting of particles with a diameter around 1 μm. The level of generated haze was linearly dependent on the concentration of RNA; however, a given amount of RNA gave different levels of haze in two different brands of European lager beers. FT-IR spectroscopy of isolated haze demonstrated the presence of RNA and protein. Analysis by SDS-PAGE showed only the presence of beer protein Z. The haze was disrupted upon ribonuclease treatment, indicating that intact polymeric RNA chains are required. The level of haze decreased as the beer ionic strength increased. Furthermore, the level of haze also decreased as the pH of the beer approached the pI of protein Z. This demonstrates that the haze was formed by electrostatic interactions between protein Z and RNA. The RNA-protein beer haze can be utilized as an alternative or supplement to current haze contributors.